Manufacture of bituminous paving.



NITED STATES 3 PATENT 7 OFFICE.

WALTER S. WILKINSON, OF BALTIMORE, MARYLAND.

MANUFACTURE OF BITUMINOUS PAVING.

SPECIFICATION forming part of Letters Patent No. 705,728, dated. July29, 1902.

Application filed December 31, 1901. Serial No. 87,930. (No'specimens)To all who-In it may concern:

Be it known that I, WALTER S. WILKINSON, a citizen of the United States,residing at Baltimore, in the State of Maryland, have invented anImprovement in the Manufacture of Bituminous Paving, of which thefollowing is a specification.

Bituminous paving or pavement mixtures or compositions ordinarilyconsist mainly of crushed and partly-pulverized stone or sand, veryfinely-comminuted stony material called dust or fines, the Whole of theforegoing being commonly known as body material, and a cementing orbinding agent commonly termed bituminous cement. This cement has beenusually an asphaltic cement containing, say, from ten to twenty percent. of residuum of petroleum or other flux mixed with the asphaltwhile heated. When the mixture or composition is to be compressed inmolds into blocks or tiles, the body material is usually crushed andpartly-pulverized stone.

When it is to be laid and rolled or tamped in the form ofsheet-pavement, the body material is usually sand and dust or fines; butwhether compressed in molds into blocks or tiles or laid and rolled ortamped in sheet form the durability of the resultant pavement dependslargely upon the thoroughness and uniformity of mixture of the variouselements composing the mixture or composition. For

instance, the body material is ordinarily re lied upon to furnish theprincipal resistance to the wear and tear of traffic, the fines are usedto fill in the voids between the coarser particles of body material, andthe cement is intended to serve merely as a binding agent between thevarious particles of stony material.

It is desirable that the voids between the coarsest particles of bodymaterial be filled by the next smaller particles, and the voids thenremaining filled by the next smaller particles, and so on, down to thesmallest voids, and these in turn filled with the fines, the cementserving merely as a coating to bind or unite every part of the surfaceof each stony particle to the surfaces of the next adjacent stonyparticles. In fact, the presence of voids filled with free cementconstitutes an element of weakness in any bituminous pavement hence thenecessity for the finest possible fines, preferably even an impalpablepowder, and the necessity, also, for a method of handling the materialsthat will insure the most thorough and uniform mixing of the bodymaterial in order to reduce the possibility of any voids remaining to befilled with free cement. Obviously there is the equal necessity for sucha method of handling or treating the materials as will insure the mostcomplete coating of each and every particle of stony material with athin film or coating of the binding agent or cement.

Prior to my invention in the actual commercial manufacture of bituminouspaving or pavement mixtures or compositions it has been customary toprepare the oement,usually an asphaltic cement, in a vessel or tank andto dry-mix in a usual pug-mill all the body material, including thefines. Then and while the dry-mixed body material was being agitated inthe pug-mill the cement was added thereto by pouring it gradually intothe agitated mass, the Whole being mixed by continned operation of thepug-mill. Asphalt being the most costly of all the ingredients orelements employed in compositions of this character, it is desirable toreduce the quantity of asphalt or asphaltic cement required for theproductionof a given quantity of suitable asphaltic paving or pavementmixture or composition as much as possible without deterioration of thequality of said mixture or composition. This can best be done byrendering more complete the uniform distribution of fines throughout themass and the more complete coating of each and every particle of suchfines with the cement in order that each of such particles may betterfulfil its function of filling a void, leaving the cement merely as asurface coating therefor.

WVhile I have found in the course of my experiments that it is desirableto first mix while dry or dry-mix the bulk of the'body material beforethe cement is added thereto,

I have discovered that the resultant mixture terial. coating with cementof each and every par ticle of the fines, however small, and which itwould be impossible to obtain if the said fines were first dry-mixedwith the remaining body material. I have found that a large percentageof thefines which it is desired to use in the mixture or composition maybe thus incorporated into the cement, while still preserving thatliquidity which is necessary to enable the cement to permeate freely themass of remaining body material. Having by this impregnation of thecement with fines obtained the most thorough possible incorporation ormixture of such fines and the ocment, this fines-impregnated cement isthen brought into contact with the remaining body material andthoroughly mixed therewith. This is ordinarily best done by agitatingsuch remaining body material in a pug-mill and while in a state ofagitation adding, preferably gradually, thereto the fines-impregnatedcement, the agitation producing a thorough and complete mixture of saidbody material and the fines-impregnated cement, and the cement beingalready thoroughly impregnated with the fines and in a liquid conditionnotwithstanding the fines it contains serves as a vehicle to carry thecoated fines into and to fill all the voids in the mass. Nor is theredanger of any material voids being filled with free cement because ofthe fines carried in and by the liquid cement. I have found also that bythus obtaining a more thorough filling of the voids with the coatedfines a given quantity of asphalt is sufficient for and will produce alarger quantity of paving or pavement mixture or composition than hasheretofore been possible, the increase or gain with Trinidad asphaltamounting to about six per cent. or more. With other and purer asphaltsor cement containing a larger percentage of fiuxflux being practicallypure bitumenthe gain is proportionately greater, because the more purebitumen there is in the cement the more fines may be incorporatedtherein. The quality of the pavement produced, Whether of block or sheetform, is also greatly improved, because the mixing or incorporation ofthe materials is more perfect in that the cement is used only as abinder, the Voids being filled with stony materials,

To illustrate the practice of my invention, what is known as Trinidadasphalt, most commonly used in the United States for pavement purposes,when dried or refined, so as to be usable forpavement compositions,ordinarily contains naturally from forty-four to forty-six per cent.,more or less, of finely-comminuted earthy matter or finessuch as aluminaand silicate of alumina-and asphaltic cement made therefrom for makingasphalt blocks and tiles usually contains about eightynine per cent.,more or less, of this dried or refined asphalt and about eleven percent. of residuum of petroleum. For sheet-pavements the cement usuallycontains about eighty-five In this way I insure the thorough.

-to preserve its shape.

per cent. ofasphalt and about fifteen per cent. of residuum. Whenasphaltic paving-cement is made from asphalts which are nearly purebitumen-such as Bermudez, Alcatrez, &c. a larger percentage of'flux isadded, because there is nearly double the percentage of bitumen in agiven quantity as compared with Trinidad asphalt. While this asphalticcement is heated to about 320 Fahrenheit, I add, in accordance with mydiscovery, a suit able quantity of dust or finely-comminuted limestoneor other earthy matter-such as brick dust, ground sand, cement, or otherfines--but preferably specially-prepared calcareous material reduced asnearly as possible to the condition of an impalpable powder.

When the asphaltic cement is composed of about eighty-nine per cent. ofdried Trinidad asphalt and about eleven per cent. of residuum ofpetroleum or equivalent percentage of other flux, I add the dust orfines to the cem ent, preferably while the latter is in a moltencondition and under agitation, in the proportion, say, of aboutthirty-five pounds of the fines to about one hundred pounds of theasphaltic cement and mix-and incorporate the same thoroughly and evenlythroughout the cement. This may be done by mechanical means or by theuse of jets of air or steam projected into the mass.

If an asphalt containing a much larger percentage of bitumen thanTrinidad is used, a much larger percentage of dust or fines can -beadded to the cement and incorporated in and with it. J

Having heated the body material other than the fines contained in thecement and placed such other or remaining body material in a usualpug-mill or mixer and dry-mixed the same, if necessary, then and whilesaid body material is still hot and agitated by the rapidly-movingblades of the mixer I take the hot asphaltic fines-impregnated cementand bring it, as by pouring, gradually into con tact with the agitatedhot body material in the mixer and rapidly and thoroughly mix the sametherewith. The resultant mixture or composition is then ready forcompression for use. under heavy pressure in a mold, and the resultantcompressed body is quickly cooled in flowing water or otherwise to setit exteriorly The compression thoroughly compacts the mass throughoutwhich the fines-impregnated cement is distributed, thus insuring themost advantageous results therefrom, and the quick cooling exteriorly ofthe compressed mass or body prevents distortion and relaxation orrecovery thereof by and during the necessarily slower cooling of theinterior portion of the mass. Both these steps are desirable forobtaining the best results from my invention when applied to themanufacture of blocks, tiles, and the like. If for sheet-pavements, saidmixture orcomposition is laid while hot and is tamped or rolled upon theroadway.

If for blocks or tiles, it is compressed I When the amount of fines thatmay be found with the body material, together with the fines it ispossible to add to thecement and still preserve its necessary liquidity,does not equal the whole amount of fines desired in the mixture orcomposition, any additional fines may be added to and dry-mixed with thebody materials, as'heretofore.

I have found ordinarily that in paving mixtures where the body materialis crushed noncalcerous stone from twelve per cent. to fifteen per cent.of finesimpregnated asphaltic (Trinidad) cement and about eighty-eightto eighty-five per cent. of remaining body material produce excellentresults; but these proportions will vary more or less, according to thematerials used and the conditions under which they are used.

mixture or composition while increased in.

quantity is also of a quality and durability superior to anything everheretofore obtained for paving purposes.

Having described my invention and without limiting myself to unessentialdetails,

what I claim, and desire to secure by Letters Patent, is-

1. Thatimprovement in the manufacture of bituminous paving or pavementmixtures or compositions which consists in first producing afines-impregnated cement by mixing bituminous cement and fines;dry-mixing by agitating the remaining body material, and then, while thelatter is in agitation, mixing therewith said fines-impregnated cement.

2. That improvement in the manufacture of bituminous paving or pavementmixtures or composition which consists in impregnating the bituminouscement with as much of the fines as maybe added thereto while stillpreserving the necessary liquidity of the cement, agitating theremaining body material, and, while the latter is in agitation, mixingtherewith said fines-impregnated cement.

3. That improvement in the manufacture of bituminous pavements whichconsists in producing a fines-impregnated cement consisting ofbituminous cement fixed with fines, agitating the remaining bodymaterial, and, while in agitation, mixingtherewith the finesimpregnatedcement, subjecting the resultant mixture to heavy compression in a moldand subjecting the compressed body to the action of a cooling agent, toset it to preserve its shape. I

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

WALTER S. WILKINSON.

Witnesses:

L. RABILLON, JAMES E. TROTT.

